A lithium ion secondary battery has characteristics of higher energy density and a smaller memory effect than other secondary batteries including a nickel-hydrogen battery and a nickel-cadmium battery. Hereby, the application of the lithium secondary battery is growing from a power supply for portable electronics such as a smartphone and a tablet terminal; a power supply for electric home appliances; a stationary power supply for power storage facility, an uninterruptible power supply system and a power leveling device; and up to a driving power supply for a ship, a train, a hybrid vehicle and an electric vehicle. Thus, further improvement in battery performance is demanded.
Among various applications of a lithium ion secondary battery, especially in the applications to a small sized power supply and a middle sized power supply for a vehicle or the like, reduction of an occupied battery volume is demanded, whereby demands for improving volume energy density of a cathode are growing. Therefore, a technique is proposed for improving packing density of a cathode active substance by appropriately controlling a particle size of the cathode active substance.
For example, Patent Document 1 discloses a method for manufacturing a lithium-containing composite oxide. This is a manufacturing method for a lithium-containing composite oxide represented by a general formula of LiwNxMyOzFa [where N is at least one kind of an element selected from a group of Ni, Co and Mn; M is at least one kind of an element selected from a group of a transition metal element other than Ni, Co and Mn, and Al, Sn and an alkaline earth metal; 0.9≤w≤1.3, 0.9≤x≤2, 0≤y≤0.1, 1.9≤z≤4.1, 0≤a<0.05].
Herein, the method includes the steps of: mixing granulated particles with a mean particle size of 10-40 μm containing at least an N element and made of primary particles with a mean particle size of 1 μm or less, crystallized particles with a mean particle size of 6 μm or less containing at least an N element, in which the weight rate of the granulated particles/the crystallized particles is 10/90-90/10, and a lithium compound so as to produce powder of the mixture; firing the resulting powder at 750-1250° C. under an oxygen-containing atmosphere; and thereby manufacturing a lithium-containing composite oxide.
Further Patent Document 2 discloses a cathode active substance for a non-aqueous electrolyte battery. The cathode active substance includes primary particles of a lithium composite oxide represented by an average composition of LixCOyNizM1−y−zOb−aXa [where M is one kind of an element, or two or more kinds of elements selected from a group of boron (B), magnesium (Mg), aluminum (Al), silicon (Si), phosphor (P), sulfur (S), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), molybdenum (Mo), silver (Ag), barium (Ba), tungsten (W), indium (In), strontium (Sr), tin (Sn), lead (Pb) and antimony (Sb). X represents halogen. “x”, “y”, “z”, “a” and “b” each represents a value satisfying relationships of 0.8<x≤1.2, 0<y≤0.5, 0.2≤z≤1.0, 0.2<y+z≤1.0, 1.8≤b≤2.2, 0≤a≤1.0].
Alternatively, the cathode active substance includes secondary particles formed by aggregation of primary particles of a lithium composite oxide, a partial surface of the primary particles being covered with an electron conductive material. The lithium composite oxide is represented by an average composition of LisM11−tM2tPO4 [where M1 is one kind of an element, or two or more kinds of elements selected from a group of iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn) and magnesium (Mg). M2 is one kind of an element, or two or more kinds of elements selected from Group 2-Group 15 excluding M1. “s” and “t” each represents a value satisfying relationships of 0≤s≤1.2, 0≤t≤1.0].
Herein, a volume-based 50% mean particle size of the secondary particles measured by a laser diffraction/scattering method is in the range from 10 μm to 30 μm, a number-based 10% mean particle size is 3 μm or less, a number-based 50% mean particle size is 6 μm or less, and a number-based 90% mean particle size is in the range from 13 μm to 20 μm.